In lead storage batteries, there are commonly used paste-type electrode plates made by coating a paste prepared by kneading a partially oxidized lead powder, water and sulfuric acid as main components, a short fiber of synthetic resin, a fine powder of carbon, organic additives and, if necessary, small amounts of other components on a continuous porous body such as a cast grid, a punching sheet, an expanded metal or the like, and, if necessary, cutting it to shapes of electrode plate, followed by drying. This electrode plate is combined with a separator and an electrode plate assembly is made therefrom. The assembly is placed in a cell, to which dilute sulfuric acid as an electrolyte is added and formation of the electrode plates is carried out in the cell. Alternatively, electrode plates are subjected to formation outside the cell and then are placed in the cell to impart a function of battery. It is generally known to add red lead, namely, Pb.sub.3 O.sub.4 which is a high grade oxide in order to avoid loss of power and time because efficiency of formation is low especially at a positive electrode in the stage of formation of electrode plate.
When red lead is applied to a paste-type electrode plate, efficiency of formation charging increases with increase in the amount of red lead and a lead storage battery made using such electrode plates is improved in initial working characteristics, but tends to deteriorate the life of the battery. Therefore, red lead is used commonly for a cladding-type electrode plates comprising a porous tube in which an active material is packed, but in practice it is hardly used for paste-type electrode plates of the type which are predominantly used at present. A few attempts have been tried to form a red lead layer on an electrode plate for a special purpose and but this has not yet been of practical use.
Generally, for mass production, red lead is prepared by further firing (oxidizing) a lead powder in which a part or the whole of lead has been oxidized into lead monoxide (PbO). Ratio of Pb converted to Pb.sub.3 O.sub.4 is taken as conversion ratio to red lead here.
The above-mentioned deterioration in life of the battery occurs under the condition that in the course of production of red lead through oxidation of a lower oxide such as lead monoxide (PbO), at least 95% of Pb is converted to red lead according to conception of grade of red lead. Red lead of such grade has been used as the additive. However, this red lead is lower in reactivity with sulfuric acid than the ordinary lead power of 60-80% in oxidation degree and besides, has a hard surface and becomes excessively porous and gives an adverse effect on binding power between pasty active materials per se at coating on a support, aging of the paste and working as a battery.
It is considered that the above properties are also influenced by graduation effect or increase of hardness of secondary particles when lead powder is exposed to high temperature for a long time at the final stage of enhancing the conversion ratio to red lead to 95%.
The object of the present invention is to solve the problem of deterioration in the life of a battery which occurs opposite to the advantage of improvement in efficiency of formation charging when the above-mentioned red lead is added to the paste.